Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $84.46   11.722%   $94.3604   $94.36   $94.35   $94.40  
  Purchase #2 $193.90   9.612%   $212.5377   $212.54   $212.55   $212.50  
  Purchase #3 $47.85   10.177%   $52.7197   $52.72   $52.70   $52.70  
  Purchase #4 $163.30   5.107%   $171.6397   $171.64   $171.65   $171.60  
  Purchase #5 $104.92   7.786%   $113.0891   $113.09   $113.10   $113.10  
  Purchase #6 $194.65   9.757%   $213.642   $213.64   $213.65   $213.60  
  Purchase #7 $145.48   4.373%   $151.8418   $151.84   $151.85   $151.80  
  7 purchase totals = $934.56       $1,009.8304   $1,009.83   $1,009.85   $1,009.70